Research articles

A Lewis-acid-catalysed 1,3-dipolar cycloaddition provides rapid access to a variety of substituted spirooxindoles. Initial cellular evaluations supports the view that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry, and decorated with assorted substituents, will be a rich source of compounds with diverse bioactivity.

Direct experimental probing of conical intersections is rare but here, in studies of the photodissociation of thioanisole, a striking dependence of the non-adiabatic transition probability on photoexcitation energy has been observed, revealing the nuclear configuration of the conical intersection and its dynamic role in such transitions.

The assembly and evaluation of molecular structures on surfaces has been boosted by advances in single-molecule techniques. The development of such methods are continued here, showing that double-stranded DNA, bound to the tip of an atomic force microscope, can be deposited on the surface of a gold electrode using an electrical trigger.

Xenon difluoride is one of the most stable noble-gas fluoride compounds with a simple linear molecular structure. It has now been shown to undergo several phase transitions at high pressures to give extended solids and even a metallic phase containing XeF₈ polyhedra.

The anomeric effect, which influences the position of polar substituents in the chair conformation of various heterocycles, is commonly rationalized using hyperconjugation. Now, by theoretically studying molecules that display the anomeric effect, strong evidence is provided that hyperconjugation is not responsible and it is better interpreted in terms of electrostatics.

Nitric oxide, NO, has an unpaired electron and is widely used and studied in such diverse fields as biochemistry and atmospheric chemistry. Its radical nature means that singly charged species are common, but now two electrons have been added to give a radical dianion in an yttrium complex.

Usable electronic devices exploiting the attractive properties of graphene will require narrow ‘nanoribbons’ of the atom-thin carbon sheets. Ribbons narrower than 5 nm are desirable for effective devices, but conventional lithography is limited to 20 nm. Now, a gas-phase chemical approach for etching graphene from the edges has produced graphene nanoribbons below 5 nm.

Although intermetallic compounds and alloys feature metal atoms bonded solely to other metal atoms, this motif is unusual in molecular compounds. Now, three compounds with lanthanide metals surrounded by transition metal atoms have been made. Although reactive, they mimic intermetallic bonding and form a conceptual link from coordination compounds.

Monomer-sequence information in synthetic copolyimides can be recognized by tweezer-type molecules binding to adjacent triplet-sequences through complementary aromatic π–π-stacking, with different tweezer molecules showing different sequence-selectivities. Single-crystal X-ray analysis of tweezer–oligomer complexes confirms the tweezer-binding selectivity, and NMR spectroscopy reveals a new mechanism (‘frameshift-reading’) for tweezer-based sequence recognition in chain-folding copolyimides.

Metal-containing fullerene cages are widely known, but hard to characterize because of their reactivity towards empty cages. Now the molecular and crystal structures of lithium-containing C₆₀ molecules have been determined.

Covalent organic frameworks (COFs) organize organic subunits into predictable and precise networks with long-range order. The limited generality of methods for COF synthesis has thus far precluded the incorporation of complex building blocks into these emerging materials. Now, a new Lewis acid-catalysed protocol for boronic ester formation provides a two-dimensional COF containing stacked phthalocyanine chromophores.

A fundamental mechanism for singlet fission, a process that may govern instances of multi-exciton generation, has yet to be described. Sophisticated calculations now show that singlet fission in pentacene proceeds through the conversion of a photoexcited state into a dark state of multi-exciton character that subsequently splits into two triplets.

The addition of a single chemical signal can trigger multiple disassembly–reassembly events in a dynamic self-assembling system that is based on the formation and exchange of both imine and metal–ligand bonds. Different metal-helicate superstructures are either created or destroyed in response to the signal as the system seeks thermodynamic equilibrium following perturbation.

Freeze-drying of aqueous myoglobin–polymer surfactant nanoconjugates affords a water-free solid that melts at room temperature to produce a viscous solventless liquid protein that exhibits near-native secondary structure and reversible dioxygen binding. The results challenge the accepted role of solvent molecules in mediating protein structure and function, and offer new opportunities in protein-based nanoscience and bionanotechnology.

Porous coordination polymers can form materials that are both crystalline and flexible, creating regular yet dynamic channels that are promising for guest sorption. Guest selectivity is difficult to achieve, however, and typically relies on size- or shape-recognition. A framework has now been assembled that combines charge-transfer interactions and structural flexibility to only accommodate O₂ and NO.

The development of benign methods for carbon–carbon bond formation is a continuing challenge. Here, a simple procedure for the hydroacylation of α,β-unsaturated esters is described, in which auto-oxidation of aldehydes and subsequent acyl radical addition to α,β-unsaturated esters occurs without the need for additional reagents.

Thermal reduction of graphene oxide is an attractive route towards the preparation of graphene, but complete removal of residual oxygen is problematic. Now, molecular dynamics simulations elucidate the chemical changes involved in this process.

In analogy to classical living polymerizations, the controlled formation of highly monodisperse cylindrical micelles — ranging from approximately 200 nm to 2 µm in length — has been demonstrated using very small and uniform crystallite seeds as initiators for the crystallization-driven living self-assembly of block copolymers with a crystallizable, core-forming metalloblock.

Converting dioxygen into more reactive species is extremely useful for direct oxygenation of organic compounds, but doing this with cheap and non-polluting elements is difficult. Now, a carbene-activated silylene has been shown to activate dioxygen, resulting in the isolation of elusive silicon–oxygen species at room temperature.

Metal–organic frameworks (MOFs) are typically built by linking metal centres with organic bridges. By using metal–diimine complexes as linkers, researchers have now immobilized these photoresponsive moieties into a MOF scaffold, which enabled them to observe a different excited state from that occurring in solution, and study a photoreaction crystallographically.